1. Field of the Invention
The present invention relates to dental glass ionomer cement, and more particularly, it relates to a dental glass ionomer cement composition in paste form constituted from a first paste and a second paste, which are mixed to exert hardening.
2. Description of the Conventional Art
Various kinds of dental cement have been used for a wide range of purposes. Representative examples of dental cement that is currently used include zinc phosphate cement utilizing reaction between zinc oxide and phosphoric acid, polycarboxylate cement utilizing reaction between zinc oxide and polycarboxylic acid, zinc oxide eugenol cement utilizing reaction between zinc oxide and eugenol, glass ionomer cement utilizing reaction between fluoroaluminosilicate glass and polycarboxylic acid, and resin cement utilizing polymerization of an acrylic monomer.
These kinds of dental cement each have advantages and disadvantages. For example, the zinc phosphate cement has such problems that it has no adhesion property to teeth, and phosphoric acid causes irritation in the initial stage of hardening; the polycarboxylate cement has such problems that a set body thereof is low in hardness; and the zinc oxide eugenol cement has such problems that it is low in strength and is inferior in durability inside an oral cavity, whereby the purpose thereof is limited to temporary sealing and temporary adhesion, and also eugenol itself has acridity. The resin cement has such advantages that the other kinds of cement does not have, i.e., excellent adhesion property and excellent mechanical strength, but there are such problems that the operationality thereof is complicated, and there remain some problems in bio-compatibility.
The glass ionomer cement is used by hardening through reaction of an acid, such as a polycarboxylic acid, and fluoroaluminosilicate glass powder in the presence of water. The glass ionomer cement has such excellent characteristics that it has considerably good bio-compatibility, a set body thereof is translucent and is excellent in esthetics, it has excellent adhesion property to teeth, such as enamel and dentin, and it has an anti-dental caries function owing to fluoride contained in the glass. Owing the characteristics, the glass ionomer cement is widely used in the field of dental surgery for filling a cavity of dental caries, cementing of a crown-inlay-bridge and an orthodontic band, a lining of a cavity, a sealer for root canal, core construction, and pit and fissure sealing.
While the glass ionomer cement has various characteristics noted in the foregoing, the ordinary dental glass ionomer cement is constituted from a powder component and a liquid component and has disadvantages of complication in operations, such as quantitation and mixing. In view of the disadvantages, the inventors have proposed a glass ionomer cement composition in paste type constituted with a first paste containing a polycarboxylic acid, water and a filler that does not react with the polycarboxylic acid, and a second paste containing fluoroaluminosilicate glass powder and a polymerizable monomer having no acid group, to which a polymerization catalyst corresponding to the polymerization method for the polymerizable monomer is appropriately added, as disclosed in Japanese Patent Laid-Open No. JP228327/1999.
However, although the glass ionomer cement in paste type is excellent in mechanical strength owing to the use of the polymerizable monomer for providing the paste type of the components containing the fluoroaluminosilicate glass, there is a possibility of adverse affect of an unreacted monomer remaining after polymerization to a living body. Furthermore, a hydrophilic thickening agent is generally used in the case where components containing fluoroaluminosilicate glass but containing no polymerizable monomer are formed into a paste. However, when the mixing amount of the thickening agent in the glass ionomer cement composition is increased, there is such a tendency that a set body thereof is decreased in mechanical strength, such as compressive strength. Therefore, it is the current situation that a paste glass ionomer cement composition using no polymerizable monomer has not yet been in practical use.